Sign of life and courage on patrol (9)
I believe the answer is:
heartbeat
'sign of life' is the definition.
'courage on patrol' is the wordplay.
'courage' becomes 'heart' (heart is a kind of courage).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'patrol' becomes 'beat' (I've seen this before).
'heart'+'beat'='HEARTBEAT'
'and' is the link.
(Other definitions for heartbeat that I've seen before include "Circulation noise" , "Essential pulsation" , "Animating force" , "Pulse of cardiac origin" .)